The present invention relates to a glass substrate for a filter disposed on a front surface of a display panel and, more particularly to a glass substrate suitable for a front filter of a plasma display panel (PDP). The present invention further relates to a display device provided with the substrate. It should be noted that the present invention may be applied to a field emission display (FED), a cathode ray tube (CRT) or any other display device than the PDP.
A plasma display device is provided with a front filter having one or more function of electromagnetic-wave shielding function, near infrared ray blocking function, and anti-reflection function (high transmittance). For improving these functions, JP H11-307987A discloses a front filter substrate which has the surface resistance of 3xcexa9 or less for the electromagnetic-wave shielding function, the transmittance of 20% or less at 850 nm wave length for the near infrared ray blocking function, and the transmittance of 60% or more in a visible wavelength range for the anti-reflection function.
Since a front filter substrate is disposed on a front surface of a display panel, the substrate should have considerable strength and light weight. The strength is fracture strength against external forces. The filer substrate requires sufficient strength for protecting the panel against eternal forces and securing a human body as it comes into contact therewith. Improving strength of the substrate generally conflicts with reducing weight thereof, and it has been difficult to satisfy both these characteristics in a front filter substrate for a display.
Since information and an image displayed on a display device are seen through a filter, deformation such as a warp and waviness which may lead to optical distortion of the filter should be prevented for improving display quality which is the primary function of a display device. Preventing deformation such as a warp conflicts with improving strength and reducing weight. That, is, when the thickness of the substrate is reduced to lower weight thereof, the rigidity of the substrate is also reduced so that the substrate is easily deformed. When the substrate is reinforced to improve its strength, particularly by a reinforcing process having a step of heating and subsequently cooling thereof, the substrate often suffers thermal deformation including a warp, whereby the display device deteriorates in its quality of display.
It is an object of the present invention to provide a filter substrate which has considerable strength, excellent display quality (due to a little warp and distortion), and reduced weight. The present invention also aims to provide a display device having the substrate.
A filter substrate for a display device of the present invention has a glass substrate and has at least one function of electromagnetic-wave shielding function, near infrared ray blocking function, and anti-reflection function. The glass substrate has a thickness between 1.8 mm and 3.2 mm, an average surface compressive stress between 20 MPa and 70 MPa, and a warp ratio of 1.0% or less. Since the filter substrate has a relatively small thickness, it is light weight. The suitable surface compressive stress of the substrate gives high fracture strength thereto. The small warp ratio gives small optical distortion and excellent display quality to the substrate.
The display device of the present invention has a display body having a face for display and the filter substrate of the present invention disposed over the face.